A camera of this type has been described in commonly owned U.S. Pat. No. 4,003,646 which also discloses means for automatically switching to the long-term mode upon sensing the lack of sufficient illumination even in the wide-open position of an associated diaphragm. In a commonly owned copending application, Ser. No. 906,862 filed May 17, 1978, I have disclosed a similar system in which, however, only the film transport is arrested for long-term exposure while the shutter continues operating at its normal rate.
In a motion-picture camera wherein the aperture of a diaphragm is controlled automatically, e.g. with the aid of a bridge circuit including a photosensor in one of its branches, fade-in and fade-out operations can be initiated by modifying the circuitry of a photometer to simulate a more intense illumination, thus causing a reduction in the diaphragm aperture. Such an aperture reduction, when coming at the end of a scene, produces a fade-out effect; for a fade-in effect at the beginning of a scene, closure of the diaphragm to an extent unrelated to the actual lighting conditions precedes the start of the picture-taking process and is then followed by a progressive reopening of the diaphragm to the degree required by the actual luminous intensity. The fade-in or fade-out time depends on the speed of the diaphragm-setting motor and may last about 36 frames or two seconds, for example.
With a camera operating in the long-term mode, fading can no longer be carried out in this manner since a reduction in diaphragm aperture--and therefore in available illumination--would automatically extend the unblocking phase of a shutter cycle and would therefore delay or possibly prevent the advance of the film to its next frame.